Glasses with Tunable Liquid Crystalline Order

液晶（LC）和玻璃是现代技术中的重要材料。LC能够通过外部控制快速调整分子组织，使其可用于显示器和传感器。玻璃将液体般的无序和空间均匀性与固体的机械强度结合在一起，在光学，电子学和非晶药物中找到了应用。该项目由固态和材料化学计划以及NSF的凝聚态物理计划支持，创造了联合收割机LC和玻璃优点的新材料-具有连续可变LC顺序的玻璃状材料。这些材料显示出在LC的有序性和玻璃的无序性之间可调的分子堆积，同时保持了普通玻璃的优点。它们有望在有机电子学和光电子学中得到应用。例如，控制广泛用于手机显示器的有机发光二极管（OLED）的有源层中的发射体分子的组织的能力可以显著提高这种显示器的效率。鉴于这些设备的数量，这是全球规模的好处。一般来说，这些新材料非常适合性能取决于分子取向和堆积的应用，但可能会受到晶体材料中常见缺陷的影响。此外，制药科学家将能够使用这些材料来优化溶解度和物理稳定性。此外，该项目通过整合材料研究和教育，促进研究生、本科生和高中生的培训。外联活动包括每年夏天通过UW-Madison PEOPLE计划向来自代表性不足的群体的高中高年级学生提供材料化学课程，每年5月通过UW推广服务向工业科学家提供名为无定形药物的短期课程，以及关于结晶和玻璃质材料的新演示科学很有趣，由亚利桑那州立大学的科学家领导的一个推广计划，并在整个凤凰城都会区提供。技术概述液晶以其快速和可逆的相变而闻名。这些转变发生的速度导致了快速冷却不会抑制LC有序化的概念，但最近的工作发现，LC转变可以在实际的冷却速率下动态地被阻止，从而允许形成具有可变LC顺序的玻璃或进入不同的LC相。该项目由NSF的固态和材料化学计划以及凝聚态物理计划支持，建立了通过玻璃制备条件控制分子组织的原则。该团队测试了一个假设，即玻璃中捕获的LC顺序的数量是由棒状LC分子的端对端旋转的动力学逮捕决定的。LC阶作为温度和冷却速率的函数进行评估通过使用实验室和同步辐射源的X射线散射。介电谱确定了分子围绕不同轴旋转的时间尺度和动力学停滞的温度。通过老化实验研究了玻璃态液晶有序度的稳定性。该项目预计将提供一个通用配方，用于选择工艺条件以控制玻璃中的LC顺序，从而产生具有增强有机电子和药物制剂性能潜力的材料。目前的LC转变理论通常不包括时间作为变量，有效地假设瞬时转变仅由热力学控制。该项目的成果将支持转化动力学发挥重要作用的理论的发展。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

NON-TECHNICAL SUMMARY Liquid crystals (LCs) and glasses are important materials in modern technologies. LCs enable rapid adjustment of molecular organization by external control, making them useful for displays and sensors. Glasses merge liquid-like disorder and spatial uniformity with the mechanical strength of a solid, finding applications in optics, in electronics, and as amorphous pharmaceuticals. This project, supported by the Solid State and Materials Chemistry program as well as the Condensed Matter Physics program at NSF, creates new materials that combine the advantages of both LCs and glasses - glassy materials with continuously variable LC order. These materials display molecular packing that is tunable between the order of a LC and the disorder of a glass, while maintaining the advantages of ordinary glasses. They are expected to find applications in organic electronics and optoelectronics. For example, the ability to control the organization of emitter molecules in the active layers of organic light emitting diodes (OLEDs), which are widely used in cell phone displays, can significantly enhance the efficiency of such displays. Given the number of these devices this is a benefit of global scale. In general, these new materials are ideal for applications where performance depends on molecular orientation and packing and but can be compromised by defects commonly present in crystalline materials. Additionally, pharmaceutical scientists will be able to employ these materials to optimize solubility and physical stability. Furthermore, the project advances the training of graduate, undergraduate, and high school students by integrating materials research and education. Outreach activities include the offering of a materials chemistry course each summer to high school seniors from under-represented groups through the UW-Madison PEOPLE program, a short course titled Amorphous Pharmaceuticals to industrial scientists each May through UW Extension Services, and new demonstrations on crystalline and glassy materials for Science Is Fun, an outreach program led by ASU scientists and delivered throughout the Phoenix Metro Area.TECHNICAL SUMMARYLiquid crystals are known for their fast and reversible phase transitions. The speed at which these transitions occur has led to the notion that fast cooling will not suppress LC ordering, but recent work has discovered that LC transitions can be dynamically arrested at practical cooling rates, thus allowing the formation of glasses with variable LC order or the access to different LC phases. This project, supported by the Solid State and Materials Chemistry program as well as the Condensed Matter Physics program at NSF, establishes the principles by which molecular organization can be controlled through conditions of glass preparation. The team tests the hypothesis that the amount of LC order trapped in a glass is determined by the kinetic arrest of the end-over-end rotation of rod-like LC molecules. LC order is evaluated as a function of temperature and cooling rate by X-ray scattering conducted using both laboratory and synchrotron sources. Dielectric spectroscopy determines the timescales of molecular rotations about the different axes and the temperatures of kinetic arrest. Aging experiments are used to study the stability of LC order in the glassy state. This project is expected to provide a general recipe for selecting process conditions to control LC order in a glass, leading to materials that have the potential to enhance the performance of organic electronics and pharmaceutical formulations. Current theories of LC transitions generally do not include time as a variable, effectively assuming instantaneous transitions controlled by thermodynamics alone. Results from this project will support development of theories in which transformation kinetics play an important role.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.